Method of plunge grinding



H. E. BALSIGER ET AL 2,864,211

METHOD OF PLUNGE GRINDING Dec. 16, 1958 Original Filed Aug. '26, 1948 2Sheets-Sheet 1 INVENTOR l/ARULD EBALSIGER BY IFHLPI-l E. Pmc:

A ORNEY Dec. 16, 1958 H, E, BALSIGE'R ETAL Z,864;2l1

METHOD OF'PLUNGE GRINDING Original Filed Aug. 26, 1948- 2 Sheets-Sheet FE1 I 54 NEW METHOD OLD METHOD RAP/D FEED RA PID FEED CHEEK FEEn CHEE KFEED ROUGH GRIND P011614 61?! ND smn xaur FIN/8H GEM/D FINISH GRIND SPARK001 SPAR K our INVENTOR 11mm 0 E. BALSIGER BY Rn PI/ 5. Pg/LE ATTORNEY2,864,21 l Patented Dec. 16, 1958 Martin!) or PLUNGEGRINDING Originalapplication August 26, 19.48, Seriali'No. 46,336,

new Patent No. 2,638,719, dated'May 19,1953. Di-

vided and this application May 14, 1953, Serial No. 355,112 3 5 Claims.(Cl. 51-289) -This invention relates to a method of grinding,particularly amethod of feeding a grinding wheel during a plungegrinding operation and isa division of application Ser. No. 46,336 filedAugust 26, 1948, now Patent No. 2,638,719, granted May 19, 1953.

Unground work pieces may be either out of round or ofif center or both.

A work piece which is off center or runs out may be perfectly round butthe portion to be ground rotates about a center other than its own.

Run out is corrected by grinding without the support of a steady rest sothat the centerof the work and the center of rotation tend to cometogether untilthey meet at a point somewhere between the originalpoints.

An out of round work piece may rotate about its own center but itssurface may be irregular.

Out of round is in process of correction throughout the grindingoperation but should be completed with the aid of a steady rest beforethe final sparkout.

This invention is concerned primarily with a method of correcting runout.

The current method of plunge grinding consists in feeding the grindingwheel against a work piece at a relatively fast feed rate without usinga steady rest, to grind the work rapidly to within a few thousandths offinished size, changing to a slower rate until the work is almost tosize. So long as grinding pressure is maintained on the work it isimpossible to eliminate run out completely. The present feed methodattempts to eliminate run out during the sparkout period when only abouta thousandth inch of stock remains. Run out in a shaft is variable, thesparkout period is fixed and when run out is greater than the amountleft for sparkout, the finished shaft or pin will not run true.

The term sparkout as used herein may be defined as a stopping of thefeed movement of a grinding wheel but continuing the grinding operationby virtue of the returning of the work to its normal position afterhaving been distorted by the force of the grinding feed. The grindingaction stops when the strain on the work has been completely relieveddue to the grinding away of the peripheral or other surface.

The method of this invention solves the problem by stopping the grindingfeed after rapidly removing a substantial amount of stock without usinga steady rest, and relieving the deflection, and most, if not all of therun out condition of the work piece. Thereafter the work is supported bya work rest and the finish grinding operation is performed with acomparatively light cut or by a succession of progressively lightercuts. The feed is stopped again just short of the desired size for therelief of any remaining run out.

It is therefore an object of this invention to provide a method wherebythe work piece is ground accurate as to angular location in the earlypart of a grinding operation thus leaving a substantial amount of stockto be removed a for providing a fine finish and accurate size andavoiding a finished surface accurate as to size but inaccurate as tocenter of rotation.

A further object is to provide a method whereby strain in a workpiecedue to grinding pressure is relieved and run out is corrected at the endof the rough grinding operation.

A further object is to provide a method whereby the finish grindingoperation and size control are effected on a surface rotating about itsown center.

A further object'is to provide a grinding feed and method by which thefeed movement of the grinding wheel is interrupted for a brief periodand then resumed at a slower rate.

Figure 1 is a plan view of a crank grindingmachine including a diagramof a hydraulic feed mechanism.

Figure 2 is a close-up of a grinding wheel in operative engagement withthe cheeks and peripheral surface of a crank pin.

Figure 3 is a chart of a novel method of grinding crank pins and otherwork pieces.

Figure 4 is a chart of the current method of performing such grindingoperations.

Numeralltl indicates the bedof a grinding machine, 11 a work carriageslidably mounted thereon. 12 and 13 are work heads mounted on carriage11 for rotatably supporting a crank shaft 14. A grinding wheel 20 isrotatably mounted on wheel support 21. .Said wheel support is slidablymounted on bed 10 for movement transversely of said crank shaft.

Transverse movement of the wheel base may be effected by a hydraulicmotor consisting of a cylinder .30, a piston 31 slidably mounted thereinand a piston 16d 32 which may be connected to wheel base 21 through alug 33. Fluid under pressure for operating said motor may be supplied bya pump 40 through a line 41 and a throttle valve 42, to a reversingvalve 43 which may be actuated to direct fluid under pressurealternately to lines 44 and 45 to the rod end and head ends respectivelyof cylinder 34 The method of plunge grinding, which is the subject ofthis application, is shown graphically in Figure 3. In the currentapplication, the steps disclosed in Figure 3 are controlledautomatically for the most part. However, since the method is notdependent for its novelty on the control means it will be described forthe purpose of simplification as a series of manually controlledoperations.

Valve 43 is shifted to direct fluid under pressure through line 45 tothe head end of cylinder 30 to move the wheel base 21 and grinding wheel20 toward the work. The speed of this movement is controlled by thesetting of throttle valve 42. The operator will set the valve for arapid feed movement until the sides of the grinding wheel engage thecheeks fit? of crank pin 51. He will then reduce the feed rate by meansof throttle valve 42 to a feed suitable for grinding said cheeks. Justbefore the grinding wheel engages the peripheral surface of the crankpin, the rate of feed will be further reduced by adjustment of valve 42to a speed suitable for rough grinding in which a substantial amount ofstock is removed in a short time. At a predetermined point in themovement of the wheel, which may be determined either by feel or by asuitable gauge, the operator closes valve 42 stopping the feedaltogether. During this rough grinding operation run-out or eccentricityis removed from the pin so that during the sparkout period, after thefeed has been stopped, the surface of the pin will be ground concentricwith its center of rotation. As soon as this has been accomplished,valve 42 may be opened to a setting to cause the feed to be resumed at arate suitable for finish grinding. When the work is ground almost tosize the feed is again stopped and the final size is reached during thesparkout. Since the run-out was removed during the rough grindingoperation the operator need be concerned only with the matter ofgrinding accurately to size during the finishing operation.

As indicated in Figure 4 the old method does not include a sparkoutoperation following the rough grinding operation and as a result theoperator has the problem of eliminating run-out as well as holding sizeright up until the final sparkout. When the amount of run-out remainingin the shaft at the end of the finish grind is greater than the amountof stock left on for sparkout,

the finished pin might be accurate as to size but will not run true toits own center and the shaft will have to be reground or scrapped.

What is claimed is:

' 1. The method of plunge grinding a workpiece which consists ineffecting a continuous rapid feeding movement of a grinding wheelagainst the workpiece, stopping said feeding movement of the wheel at apredetermined point for a selected interval to relieve the work from thestress imposed by the rapid feeding movement, continuing the grindingoperation by the Wheel in fixed position upon the work, freed from thestress produced by said rapid feed movement and finally resuming saidfeed until a predetermined size is reached.

2. The method of plunge grinding a workpiece which consists in effectinga rapid feeding movement of a grinding Wheel against the workpiece torough grind it, stopping said feeding movement of the wheel at apredetermined point for a selected interval to permit the work tosparkout to correct any out of round condition, and thus find its owncenter and finally resuming the feeding movement at a slower finegrinding rate until the final size is reached.

3. The method of plunge grinding a workpiece which consists in effectinga rapid feeding movement of a grinding wheel against the workpiece torough grind it, stopping said feeding movement of the wheel at apredetermined point and for a predetermined time to permit the Work tosparkout and finally resuming said feeding movement at a slower finegrinding rate in a series of steps, said steps being initiated inresponse to predetermined changes in size of the work.

4. The method of plunge grinding a workpiece which consists in effectinga rapid feeding movement of a grinding wheel against the workpiece torough grind it, stopping said feeding movement of the wheel at apredetermined point for a predeterined time to permit the work tosparkout and finally resuming said feeding movement at a slower finegrinding rate in a series of steps at progressively slower speeds untilthe final size is reached.

5. The method of plunge grinding a pin on a crankshaft which consists infeeding a grinding wheel against the crankshaft at a relatively rapidrate during the grinding of the crank cheeks, rough grinding the pin ata reduced feed rate and starting the flow of coolant, stopping thefeeding movement for a sparkout period to permit the work to find itsown center, resuming the grinding feed, at a further reduced rate untila predetermined size is reached, continuing the feeding movement at astill further reduced rate until a second predetermined size is reached,and stopping the feeding movement for a second sparkout until the finalsize is reached.

References Cited in the file of this patent UNITED STATES PATENTS1,914,647 Raule June 20, 1933 2,036,658 StOWell Apr. 7, 1936 2,220,490Ott et al. Nov. 9, 1940 2,638,719 Balsiger et al. May 19, 1953 FOREIGNPATENTS 626,643 Great Britain July 19, 1949

